Pneumonia is a respiratory problem in which lungs get swollen. Pneumonia is a disease of either one or both lungs that is frequently caused because of viruses, bacteria, parasites or fungi. In case of very severe condition, pneumonia can make a person very ill or even cause death. Pneumonia is characterized primarily by swelling of the alveoli in the lungs or by alveoli that are filled with liquid (alveoli is basically a microscopic pouch in the lungs that absorb oxygen). Bacteria and viruses are the main causes of pneumonia. When a healthy person inhales pneumonia causing germs into his/her lungs and his/her body's immune system cannot avoid entry, the organisms inhabit in tiny air sacs called alveoli and go on multiplying. As the body sends white blood cells to attack the infection, the sacs become filed with fluid and pus and finally cause pneumonia.
Though the infection can take place also in young and healthy people, but it is most dangerous for babies, elderly people, smokers and persons with other chronic illnesses, especially lung problems or weakens immune systems. In earlier days, before the discovery of antibiotics, most of the people who developed pneumonia consequently died due to severe infection. But now, after discovery of pneumonia antibiotics although most of these people recover, but still about 5% will die from pneumonia.